The introduction of stored program controlled communication networks is allowing the common carriers to offer many automated special services to the subscribers. It has been suggested that various automated special services be offered to the called subscriber; these services including identification of the number of the calling party, options to accept calls and requests to transfer or forward calls to a third party.
One common attribute of these special services is that the called subscriber makes the service request after answering the call. Typically, the called party, upon anwering the call, sends an appropriate dialing digit (multifrequency signal) to request a special service register in the carrier office and then sends digits to the register to identify the special service desired. It is often advantageous to the called subscriber, in the provision of these services, that there be an opportunity for request for service to be made (and the service performed) before any talking connection is completed to the calling party. Accordingly, with respect to the provision of these services, apparatus is interposed between the calling and called parties to recognize or detect requests for service. This apparatus functions, in part, to preclude the completion of the connection between the parties, for some predefined interval of time, to provide the called party an opportunity to make a request for service and to enable the service request to be identified and handled. This apparatus, however, tends to be complex and expensive and, in addition, to be nonstandard equipment requiring substantial change in central office arrangements and program procedures.
It is therefore an object of this invention to provide handling of special service requests from called subscribers without substantial modification of office equipment and procedures.
Stored program controlled switching offices have utilized ringing control circuits to provide ringing signals to the called subscriber, to recognize or sense the answer of the subscriber and to thereupon trip the ringing. The connection is completed by the office common control equipment upon scanning the condition of a ringing control circuit sensing device, which condition manifests the answering of the call.
It is another object of this invention to improve ringing control circuits to provide appropriate procedures for detecting or recognizing requests for special services from called subscribers.